The present invention relates to methods of manufacturing semiconductor devices and in particular to a method for producing high speed, low-leakage, radiation hardened CMOS/SOI semiconductor devices.
Various military and commercial applications of semiconductor devices use the devices in environments where they are or may become exposed to radiation. For example, communications equipment carried an orbiting satellite may be exposed to high levels of radiation. Radiation exposure may also occur when the devices are employed in nuclear environments such as in nuclear power plants and medical equipment utilizing radioactive materials. Conventional semiconductor devices exposed to such radiation may be destroyed or at a minimum rendered inoperative.
The use of bulk silicon to fabricate radiation hardened devices results in latch-up, well and junction depth control problems and field inversion threshold voltage control problems. To overcome these problems, methods have been devised to produce radiation hardened semiconductor devices. One such method uses silicon on insulator (SOI) materials as a substrate on which the semiconductor devices are fabricated. Methods utilizing this material exhibit the benefits of intrinsic isolation of devices on a single semiconductor chip, absence of parasitic bipolar paths, and reduced active carrier generation in a radiation environment. With this method, N- and P-channel devices are fabricated by means of a silicon etching procedure to form islands. The disadvantage of this method is that polysilicon conductor lines crossing sharp island edges generate leakage currents after reasonably high dosage irradiation, typically on the order of 100 to 200 KRad.
Consequently, there has heretofore existed a need for an improved method of manufacturing radiation hardened semiconductor devices that provide radiation hardened devices operating at relatively high dosage levels, on the order of 10 MRads, for example. Furthermore, it would be an advantage to provide an improved method of manufacturing radiation hardened semiconductor devices that embodies the advantages of both the bulk and silicon on insulator (SOI)methods while simultaneously obviating the disadvantages thereof.